Background: Present developments in Nuclear Magnetic Resonance (NMR) imaging techniques strive for improved spatial and temporal resolution performances. However, trying to achieve the shortest gradient rising time with high intensity gradients has its drawbacks: It generates high amplitude noises that get superimposed on the simultaneously recorded electrophysiological signals, needed to synchronize moving organ images. Consequently, new strategies have to be developed for processing these collected signals during Magnetic Resonance Imaging (MRI) examinations. The aim of this work is to extract an efficient reference signal, from an electrocardiogram (ECG) that was contaminated by the NMR artefacts. This may be used for image triggering and/or cardiac rhythm monitoring.

For improving sensitivity of nuclear magnetic resonance (NMR) measurements, an in-field preamplifier in a low-cost CMOS process is presented. It is based on a second-generation positive current conveyor (CCII+), with an impedance-matching output stage. The circuit has been designed with optimization of key performances, such as bandwidth, noise, and offset voltage. There have also been precautions taken against potential effect of strong magnetic field under which the circuit should operate. The designed preamplifier has a voltage gain of 15 dB and a bandwidth of 100 MHz. After fabrication of the circuit, we have carried out testing work, including in-field circuit test and characterization of MOS transistors. Under 2-T magnetic field, there have not been substantial changes in overall circuit performances compared to results obtained by post-layout simulations. For an experiment of NMR measurements with and without in-field preamplifier, the circuit is coupled with a receiver micro-coil. The experiment has been to detect protons at 85.13-MHz resonance frequency under 2-T magnetic field with water sample. The obtained results have shown a 14-dB signal-to-noise ratio improvement when the preamplifier is associated with the receiver coil.Index Terms-Current conveyor, in-field preamplifier, nuclear magnetic resonance (NMR) active probe, receiver micro-coil.

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